1. Field of the Invention
The present invention relates to a potentiometer, and, more particularly, to a potentiometer with two resolutions.
2. Description of the Related Art
A resistor is a passive electrical component that exhibits electrical resistance as a circuit element. Resistors allow a current flow proportional to the voltage placed across it. Resistors may have a fixed resistance or a variable resistance—such as those found in thermistors, varistors, trimmers, photoresistors, humistors, piezoresistors, and potentiometers.
Potentiometers are common devices used in industry, often informally referred to as a “pot”, and is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals of the potentiometer are used, one end and the wiper, it acts as a variable resistor or a rheostat.
Potentiometers are commonly used to control elements of an electrical circuit allowing their use for purposes such as volume controls on audio equipment. Potentiometers operated by a mechanism can be used as position transducers, for example, in a joystick. Potentiometers are typically used to directly control small amounts of power.
Potentiometers include a resistive element, a sliding contact, also called a wiper, that moves along the element, making good electrical contact with part of the resistive element, electrical terminals at each end of the element, a mechanism that moves the wiper from one end to the other, and a housing containing the resistive element and the wiper.
Some potentiometers are constructed with a resistive element formed into an arc of a circle usually a little less than a full turn and a wiper slides on this element when rotated, making electrical contact. The resistive element, with a terminal at each end, is flat or angled. The wiper is connected to a third terminal, usually between the other two. For single-turn potentiometers, the wiper typically travels just under one revolution as it traverses the resistive element.
Another type of potentiometer is the linear slider potentiometer, which has a wiper that slides along a linear element instead of rotating. An advantage of the slider potentiometer is that the slider position gives a visual indication of its setting.
The resistive element of potentiometers can be made of graphite, resistance wire, carbon particles in plastic, and a ceramic/metal mixture in the form of a thick film. Conductive track potentiometers use conductive polymer resistor pastes that contain hard-wearing resins and polymers, and a lubricant, in addition to the carbon that provides the conductive properties.
Potentiometers are often used within a piece of equipment and are intended to be adjusted to calibrate the equipment during manufacture or repair, and are not otherwise adjusted. They are usually physically much smaller than user-accessible potentiometers, and may need to be operated by a screwdriver rather than having a knob. They are usually called “preset potentiometers” or “trim pots”. Some presets are accessible by a small screwdriver poked through a hole in the case to allow servicing without dismantling.
Multi-turn potentiometers are also operated by rotating a shaft, but by several turns rather than less than a full turn. Some multi-turn potentiometers have a linear resistive element with a sliding contact moved by a lead screw; others have a helical resistive element and a wiper that turns through 10, 20, or more complete revolutions, moving along the helix as it rotates. Multi-turn potentiometers often allow finer adjustments relative to the rotation of a rotary potentiometer.
Some potentiometers have dual resolutions with a mechanism that switches between the resolutions by some action of the operator. For example some potentiometers have a course resistance adjustment by turning a knob, then by pulling the knob to a detent position the resistance adjustment continues at a finer rate. Pressing the knob back to the original position changes the resolution back to the course position. This type of mechanism is expensive, takes up space and is subject to failure.
What is needed in the art is an easy to operate, and inexpensive to manufacture, potentiometer having dual levels of resolution.